Like all those wacky people out there who need to fill up all their available free time with extremely time-consuming hobbies, I keep tropical fish. One of the tasks that keep my fish happy and healthy is a regular water change. I do this by removing water from the aquariums using a siphon hose. I was always told that siphons drain liquids from the reservoir to another container (placed so the surface of the drained water is lower than that of the reservoir) because air pressure is pushing down on the surface of the liquid. This is the same explanation given for how flush toilets work. But is this really true? How would you test this?

The chemists (who are pretending to be physicists in this video) at the University of Nottingham recently published a paper showing that siphons do not rely on air pressure to move liquids -- and they showed this by using a siphon in a vacuum. Unfortunately, like most scientific papers, this one is sequestered behind a paywall, so no one has read it. Including none of us toilet-flushing aquarists! But thanks to this new video, we can enjoy a special one-on-one demonstration and explanation of this experiment that refutes the original incorrect explanation that we'd always been told when we were innocent kids:

This video explains this (not freely available) paper:

Adrian L. Boatwright, Simon Puttick, and Peter Licence. (2011). Can a Siphon Work In Vacuo?Journal of Chemical Education doi:10.1021/ed2001818